The methods of encoding history for CMC can be grouped into two categories.
The first category of methods simply append the selected history to the input question, thus converting the CMC problem into a single-turn MC problem [1]}, [2]}.
There are some variants where history is first encoded into feature vectors before being appended.
For example, [3]} augment BiDAF to encode dialog context from previous \(M\)  QA pairs as follows. First, the input question embedding is extended by appending a feature vector that encodes dialog turn number. Then, the passage embedding is extended by appending a feature vector that encodes the locations of the previous answer spans.
